Baluns may be used in circuits for transforming an unbalancing signal into a balanced signal, and vice versa. This may be achieved through the use of balanced transformers to provide for an equal amplitude division and phase differential. In other words, a single, unbalanced signal may be split into two separate, balanced signals that are one hundred and eighty degrees out of phase.
Such balancing may be achieved by utilizing a coupled-line structure, in which an input line (that receives the unbalanced signal) is electromagnetically coupled through separate transformers to two separate output lines. The unbalanced incoming signal is transformed (through transformers formed by the coupled lines) into two separate balanced signals which are one hundred eighty degrees out of phase. In a particular embodiment known as a Marchand balun, the input line that receives the unbalanced signal remains open on one end, which allows the balun to be used with a wider range of bandwidths than otherwise possible.
However, conventional baluns have a myriad of problems and limitations. In particular, conventional baluns have a loss problem due to the current path that connects the coupled lines to ground. Additionally, the bandwidth of the balun may be constrained by the capacitive coupling that can occur between the coupled lines and the ground, thereby limiting the operation of the balun.